Shortstopping vinyl chloride polymerizations with styrene and its derivatives



Patented Nov. 4, 1952 2,616,885 i C E.

S-HORTSTOPPING. VINYL CHLORIDE POLY- MERIZATIONS WITH STYRENE AND. ITS

DERIVATIVES Leonard F. Marcus, Waterbury, Comm, assignor to 'United States Rubber Company, New York, N. Y., a corporation of New Jersey No Drawing. Application July 10, 1951,

Serial No. 236,073

This invention relates to improvements in.

vinyl chloride polymerizations.

The polymerization of liquefied vinyl chloride is generally carried out at mildly elevated temperatures, about 40 C. to 60 C., in an aqueous medium under a pressure substantially equal to its saturated vapor pressure, 1. e. about 4 to 9 atmospheres, in the presence of a polymerization catalyst. Pressures referred to herein are absolute pressures. The polymerization is generally carried to range of about 60% to 95% conver+ sion of monomer to polymer. All percentages and parts referred to herein are by weight. The polymerization as is well known may be an emulsion polymerization (see Mark et a1. U. S. Patent 2,068,424, and German Plastics Practice by De Bell, Goggin, and Gloor, published by De Bell and Richardson, Springfield, Mass, 1946, pages 57-66), or a granular polymerization (see Lightfoot U. S. Patent 2,511,593, and German Plastics Practice, pages 66-73, and the article by Ruebensaal on "Vinyl Resins in Chemical Engineering for December 1950, vol. 57, pages 102 to 105). After conversion of the desired amount of monomer to polymer, residual unreacted monomeric vinyl chloride is removed and the polyvinyl chloride collected by various means,

such as by coagulation or spray drying in the case of aqueous emulsion polymerization, or 'by filtration in the case of aqueous granular polymerization. The resulting polyvinyl chloride is usually washed with water and dried. If the polymerization goes beyond the desired conversion, a polymer having properties inferior to those desired in the final product may result, particularly as regards heat and light stability. To avoid this, the batch is generally cooled after the desired conversion. Undesirable post-polym erization may also take place in the blow-down tank or in the stripper where unreacted vinyl chloride monomer is removed. At the end of the polymerization, it may be necessary to store or hold the polymer-batch for some time without cooling before removing unreacted vinyl chloridemonomer. In this case the polymerization may continue during storage and thus give a product of too high conversion and of resultant undesirable properties. Also, when the unreacted 20 Claims. (Cl. 26092.8)

partial conversion of polymerizable monomer to polymer has taken place and to prevent any further polymerization of the residual unreacted vinyl chloride monomer.

I have found that styrene and substituted styrenes are effective shortstopping agents for vinyl chloride polymerizations.

In carrying out the present invention, the styrene or substituted styrene (e. g. chlorostyrenes, alpha-alkyl styrenes, alpha-alkyl chlorostyrenes) is added to the polymerization reaction after partial conversion of polymerizable monomer to polymer (usually after about 60% to 95% conversion) and thereafter the unreacted vinyl chloride polymer is removed from the aqueous medium, and the polyvinyl chloride recovered in the usual manner. Examples of shortstoppers that may be used according to the present invention are styrene, monochlorostyrene, polychlorostyrenes,-- e. g. 3,4-dichlorostyrene and pentachlorostyrene, alpha-alkyl styrenes, e. g. alpha-methyl styrene, and alpha-alkyl chlorostyrenes, e. g. alpha-methyl 3,4-dichlorostyrene, and mixtures thereof. It is completely surprising that styrene and substituted styrenes will act as shortstopping agents for aqueous vinyl chloride homopolymerizations even though they are disclosed as shortstopping agents for organic solvent polymerization and aqueous polymerization of the binary copolymerization of vinyl acetate and a minor proportion of vinyl chloride (6.8. Patent 2,512,472), in view of the known binary copolymerization of vinyl chloride and styrene in bulk and organic solvent polymeriza-;

tions as described in U. S. Patents 2,012,177 and 2,532,727. Small amounts of styrene or substituted styrenes may satisfactorily be used to shortstop the polymerization reaction, the amount effective to shortstop the polymerization generally being less than 2% based on the original vinyl chloride monomer used. For practical purposes, the amount of shortstopper may be between 0.05% and 1% by weight of the original vinyl chloride monomer used.

The polymerization reaction is carried out in the presence of a conventional free radical type polymerization initiator, such as a peroxygen or azo catalyst. Examples of peroxygen catalysts are inorganic peroxides, e. g. hydrogen peroxide and persalts, such as alkali persulfates, alkali perborates, alkali percarbonates; and organic.

peroxides, e. g. diacetyl peroxide, dibenzoyl peroxide, acetyl benzoyl peroxide, lauroyl peroxide, cumene hydroperoxide, tertiary butyl hydroperoxide." Examples of azo catalysts are alpha, alpha-azobisisobutyronitrile, and p mthoxybenzene diazo thio-Z-naphthyl ether. Catalytic amounts from 0.05% to 2% based on the vinyl chloride monomer may be used.

Tests showing the efiectiveness of the chemicals of the present invention as shortstopping agents for vinyl chloride polymerization were carried out according to the following procedure: Into each of a number of crown capped bottles equipped with self-sealing liners was placed a typical granular polymerization recipe using a water-soluble catalyst (100 parts of liquefied vinyl chloride, 320 parts of water, 0.3 part of potassium persulfate and small amounts of bufiering and wetting agents). Polymerizations were carried out at 465 C. With each shortstopping test, two polymerizations served as controls to show the conversions at an intermediate polymerization (about five and one-quarter hours) and at a final polymerization (about nine and three-quarter hours) without shortstopping agent. Atth-eend of the intermediate andfin-al polymerization times, monomeric vinyl chloride was immediately vented'andpercent conversions were obtained. In the testpolymerizations, 0.3 part and 0.5 part of styrene (based on 100 parts. of vinyl chloride monomer used) were added to separate polymerization bottlesat the same time as the. intermediate control polymerizations and the heating was continued tothe same overall time as the final control polymerization. Vinyl chloride monomer was then vented, and percent conversions were obtained by weighing the polymer.

The percent conversions ofmonomer to. polymer of the control after the intermediate and final polymerization times, and the percent conversions at the final polymerization times where the styrene shortstoppers of the present invention were added. at the. intermediate conversion times, are shown in the following-table:

Shortstopper added at intermediate conversion Intermediate Final Conversion (percent) Series A:

None (intermediate control) None (final control)- 0.3 part styrene 0.5 part styrene Bottle.polymerizations.-similar to the above were run at 52 C..wi'th atypical. granular poly-- Conversion (percent) Shortstopper added at intermediate conversion Intermediate 7 Final Series 13:

None (intermediate-control) None (final control) 0.3 part styrene." 0.6 part styrene Series None (intermediate control) i Series D:

None (intermediate control) None (final control)" 1 part 3,4'-dichlorostyrene 1 part alpha-methyl 3,4-dichlorostyrene The above work; shows .that -.the.-styrene and substituted styrenes of the present invention are effective shortstopping agents for aqueous vinyl chloride polymerizations (the experimental error in the work may be five percent). In aqueous emulsion and granular polymerizations, the polymerization reaction will generally be stopped at 60% to conversion of monomer to polymer. With the shortstopping agents of the present invention, the polymerization reaction may be stopped at any desired conversion.

In emulsion polymerizations, it is a simple matter to withdraw a sample from the reaction chamber from time to time and to analyze it for total solids in order to determine the percent conversion. On the other hand, it is almost impossible to follow the conversion in a granular polymerization by sampling, because the polymer formed separates so rapidly that a representative sample cannot be obtained. Thus other methods of determining the amount of conversion, and thereby thepoint at which the reaction should be stopped, must be used in following polyvinyl chloride granular polymerizations. For example, the heat evolved in the reaction mixture can be measured andbe directly correlated with the extent of conversion via the. known heat of reaction. Also experience has shown that polyvinyl chloride of good physical characteristics may be obtained by stopping the reaction at the pressure drop which is at the point Where the liquid vinyl chloride monomer. disappears (see German Plastics Practice, pages 61 and 77). In systems where the temperature in the reactor is automatically maintained by regulation of the jacket temperature, the pressure drop will be evidenced by a sudden pressure fall. In systems where the pressure. in the reactor is automatically maintained by regulation of the jacket temperature, the pressure drop Will be evidenced by a rapid rise in jacket water temperature, whereupon the system is thrown out of automatic control and cooling water is introduced into the jacket resulting in the usual fall of pressure in the reactor. Such methods other than sample analyses of determining when to shortstop the reaction at the desired conversion may be used in emulsion polymerization as well as in granular polymerization. The evolution of heat or the viscosity characteristics may be followed in mass polymerization to determine the point at which the shortstopping agent should be added.

The following illustrates 1711851153 of the shortstoppers of the present invention in batch aqueous vinyl chloride polymerizations. A typ, ical emulsion polymerization recipe which uses a water-soluble catalyst.(1'00 parts of liquefied vinyl chloride, 200 parts of water,. 0.2 part of potassium persulfate. and 1.5parts of. surfaceactive emulsifying agent), ora typical granular.

polymerization recipe using; a water soluble catalyst parts of liquefied vinyl chloride, 300 parts of water, 0.3 part-of potassium persulfate, and a'small amount of buffering and :Wetting agents),..or a typical granular polymerization recipe using, a monomer-soluble catalyst (100 parts of liquefied vinylchloride,- 300 parts. of water,0.5 part of lauroyl peroxide and a small amount of suspending agent) is agitated in a closed jacketed aeaction veseel. The catch is initially, heated to the=desired reaction temperature between-40 C. and 60 C. and maintained at the desired temperature-during the polymerization. The pressure in. the reactor at. such temperatures will befrom 4 to 9 atmospheres until theliquid. vinyl chlorideispolymerized and the pressure drops. After the pressure starts to drop and before it drops 2 atmospheres, 0.05 to 1 part of styrene, monochlorostyrene, dichlorostyrene, pentachlorostyrene, alpha-methyl styrene, or alpha-methyl dichlorostyrene per 100 parts of original vinyl chloride used is added so that undesirable further polymerization is prevented. Alternatively, the shortstopping agent may be added at any desired conversion at the discretion of theioperator. When the desired conversion has been reached and the shortstop added, the batch, may. be transferred to the blow-down or storage tank, held there any desired. length of time, and-then transferred to the stripper when desiredfor removal of residual unreacted vinyl chloride monomer. Finishing operations after residual monomer removal are conventional as describedin the literature references referred to above."v The shortstopping agents of the present invention give a greate uniformity of polymer properties, and alsoresult in polymers havingenhanced heat'and light stability, I I 1 In view of the many changes and modifications that may be made without departing from the principles underlying the invention, reference should be made to the appended claims for an understanding of the scope; of the protection afforded the invention;

-Having thus describedmy invention. What I claim and desire to protect by Letters Patent is: "-1.jIn the process of preparing polyvinyl chloride polymer by the polymerization of vinyl chloride in an aqueous medium, the step comprising. adding a small amount of material selected from the group consisting of styrene, 1 nuclear-substituted ohlorostyrenes, alpha-,alkylsubstitutedstyrenes, and alpha-alkyl substituted nuclear chloro-substituted styrenes to the reaction mixture during polymerization to stop the,

same. after partial conversion of polymerizable monomeric material to polymeric material.

2; In the processof preparing polyvinyl chloride-byathe polymerization of vinyl chloride in an aqueous medium, the stepcomprising adding a small amount of styrene to the reaction mixture' during polymerization to stop the same after partialconversion of polymerizable monomeric material topolymeric material. v

'3. In .the process .ofpreparing polyvinyl chloride by the polymerization of vinyl chloride in an aqueous medium, the step comprising adding a small amount of a chlorostyrene to the reaction mixture during polymerization to stop the same after partial conversion of polymerizable monomeric material to polymeric material.

4. In the process of preparing polyvinyl chloride by the polymerization of vinyl chloride in an aqueous medium, the step comprising adding a small amount of monochlorostyrene to the reaction mixture during polymerization to stop the same after partial conversion of polymerizable monomeric material to polymeric material.

5. In the process of preparing polyvinyl chloride by the polymerization of vinyl chloride in an aqueous medium, the step comprising adding a small amount of a polychlorostyrene to the reaction mixture during polymerization to stop the same after partial conversion of polymerizable monomeric material to polymeric material.

6. In the process of preparing polyvinyl chloride by the polymerization of vinyl chloride in an aqueous medium, the step comprising adding a small amount of a dichlorostyrene to the reaction mixture during polymerization to stop the same after. partial conversion of polymerizable.

monomeric. material to polymeric. material.

7..In theprocess of preparing polyvinyl chlo-* ride by the polymerization of vinyl chloride inan aqueous medium, the step comprising adding a small amountof pentachlorostyrene. to the re-v action-mixture duringpolymerizationto stop the same after partial conversion of polymerizablemonomeric material to polymeric material.

8. In the process of preparing polyvinyl chlo ride by the polymerization of vinyl chloride-in an aqueous medium, the step comprising adding a 7 aqueous medium, the step comprising adding asmall amount of alpha-methyl styrene to thereaction mixture during polymerization to stopthe same after partial conversion of polymerizable monomeric material to polymeric material. 1

10. In the process of preparing polyvinyl chlo-.

ride by the polymerization of vinyl chloride in an aqueous medium, the step comprising adding 0.05% to 1% of material selected from the group consisting of styrene, nuclear-substituted chlorostyrenes, alpha-alkyl substituted styrenes, and

alpha-alkyl substituted nuclear chloro-substir tuted styrenes based on the weight of the original" monomeric vinyl chloride used, tothe reaction mixture during polymerization to stop the same after about 60% to conversion of vinyl chloride monomer to polyvinyl chloride. I

polymerizing conditions in an aqueous medium in alpha-alkyl substituted nuclear chloro-.substi-.-

tuted styrenes to stop polymerization of unreacted vinyl chloride monomer, and thereafterremoving unreacted vinyl chloride from the aqueous medium.

12. The method of preparing polyvinyl chloride whichcomprises subjecting vinyl chloride to polymerizing conditions in an aqueous medium in the presence of a peroxygen catalyst, and after partial conversion of vinyl chloride monomer to polyvinyl chloride adding to the polymerization reaction a small amount of material selected from the group consisting of styrene, nuclearsubstituted ohlorostyrenes, alpha-alkyl substituted styrenes, and alpha-alkyl substituted nuclear chloro-substituted styrenes to stop polymerization of unreacted vinyl chloride monomer, and thereafter removing unreacted vinyl chloride from the aqueous medium.

13. The method of preparing polyvinyl chloride which comprises subjecting vinyl chloride to polymerizing conditions in a closed vessel in the presence of a peroxygen catalyst in an aqueous medium at a temperature between 40 C. and 60 C. under a pressure substantially equal to saturated vapor pressure of about 4 to 9 atmospheres, and after the pressure begins to drop and before it has dropped 2 atmospheres adding to the polymerization reaction a small amount of acrea e:

material. selected: from: the-group: consisting-of nuclear substituted: chlorostyrenes,

pheres; and after'zthe'ipressure beginsto drop and before .itrhasdroppedzZ: atmospheres adding to the polymerization?.reactionsa' small amount of styrene to stop; polymerization of unreacted vinyl chloride monomer, and thereafter removing unreactedz'vinyl chloride from the aqueous medium;

15;:The method of preparing polyvinyl chloride which comprisessubjecting vinyl chloride to polymerizing conditions in'a closed vessel in the presenceofraperoxygencatalyst in an aqueous medium at a temperature between 40 C. and 60 C. under a pressure substantially equal to its saturated vapor pressure of about 4 to 9 atmospheres, and afterthe pressure begins to drop and before it hasidroppe'd 2 atmospheres adding to the polymerization reaction a small amount of a chlorostyrene .to stop polymerization of .unreactedvinyl chloride monomer, andthereafter removing unreacted vinyl chloride from theaqueousmedium.

16. The method of. preparing polyvinyl chloride I which comprises subjecting .vinyl chloride-to polymerizing conditions: in a closed vessel in the presence of a-peroxygen catalyst in an aqueous mediumlat. a-temperature between 401 C. andGO" C. under a pressure substantially equal to its satu-' ratedlva'por pressureoraboute to 9 atmospheres, and after the pressure begins to drop and before it has dropped 2 atmospheres adding to the polymerization reactionasmall amount of monochlorostyrene to stop polymerization of unreacted vinyl chloride monomer, and thereafter removing unreacted vinyl chloride. from the aqueous medium;-

17." The method of. preparingpolyvinyl chloride which comprises subjecting vinyl chloride to polymerizing conditions in a closed vessel in the presence of a peroxygen catalyst in anaqueousmedium at as temperaturebetween- 40 'Cfand- 60 C;

under a pressure substantially .equal to "its 'satu-r rated vapor pressure of about' i-to 9 atmospheres,- and after. the pressure begins "to' drop and' before it has'dropped 2 atmospheres adding to the polye' merization reactiorra small amountof a 'polychlorostyrene to stoppolymerization of unreacted vinyl chloride monomer; and'thereafter removing unreactedivinyl chloride-from the. aqueous medi- 18. The method of preparing polyvinyl chloride which comprises subjecting vinyl chloride to polymerizing conditions in. a closed vessel in-thepresence of aperoxygen catalyst in an aqueous-medium-at atemperature between 40 C, and' 60" C.

under a pressure substantially "equal to itssaturatedivapor pressure of about 4 to Qatmospheres, and "afterthe pressure begins to drop 'andlbeio're it has dropped 2 atmospheres adding to :the poly= merization reaction a small amount of aldi'chloro styrene to stop polymerizationiof unreactedvinyl I chloride monomer, and. thereafter removin'gcuni reacted vinyl chloride fromthe aqueous medium;

19. The method of preparmgpolyvinyl chldride which comprises subjectingvinyl chloride to f polymerizing conditions in a closed vessel in the presence of a peroxygencatalyst in an aqueous medium at a temperature between 40 C. and 60 C. under a pressure substantially equalto itssaturated vapor pressure-of about 4 to 9atmosphere's, and after the pressure begins to drop and before it has dropped 2 atmospheres adding tothe polymerization reaction a small amount of analpha-alkyl styrene to stop polymerization of unreacted vinyl chloride monomer-, and thereafter removing unreacted vinyl chloride from the aqueous medium.

20. The methodof preparing polyvinyl chloride which comprises subjecting vinyl chloride topolym'erizing conditionsin' a closed vessel in the presence of a peroxygen catalyst inan aqueous medium at a-temperaturebetween 40 C. and 60 C; under a pressure substantially equalto its satu rated vapor pressure of about 4 to Qatmospheres, and after the pressure begins to drop and before it has dropped-2 atmospheres adding to' the polymerization reaction a small amount-10f i alphamethyl styrenev to stop polymerization of 1111115 acted vinyl chloride. monomen and thereafter: re-

movingc'unreacted vinyl chloride 'from the aqueous: medium:

LEONARD F; MARCUS.-

Noreferences cited. 

1. IN THE PROCESS OF PREPARING POLYVINYL CHLORIDE POLYMER BY THE POLYMERIZATION OF VINYL CHLORIDE IN AN AQUEOUS MEDIUM, THE STEP COMPRISING ADDING A SMALL AMOUNT OF MATERIAL SELECTED FROM THE GROUP CONSISTING OF STYRENE NUCLEAR-SUBSTITUTED CHLOROSTYRENES, ALPHA-ALKL SUBSTITUTED STYRENES, AND ALPHA-ALKYL SUBSTITUTED NUCLEAR CHLORO-SUBSTITUTED STYRENES TO THE REACTION MIXTURE DURING POLYMERIZATION TO STOP THE SAME AFTER PARTIAL CONVERSION OF POLYMERIZABLE MONOMERIC MATERIAL TO POLYMERIC MATERIAL. 